1. Field of the Invention
The invention relates to radio frequency (RF) pulse modulation, particularly with respect to utilization of an RF PIN diode attenuator pulse generator.
2. Description of the Prior Art
The RF PIN diode attenuator is known in the prior art for generating a pulse modulated RF carrier for use, for example, in testing the characteristics of radio frequency receivers. Such attenuators utilize the P-Intrinsic-N type diode (PIN diode). Such prior art devices generate an RF pulse by applying an RF carrier to the RF input port of the attenuator and applying a bias signal to the PIN diode to control the attenuator from maximum to minimum to maximum attenuation thereby generating an RF pulse at the output port of the device. Such prior art RF pulse generators do not control the shape of the modulated pulse. Additionally, the techniques utilized in the prior art introduce transients into the modulated signal. Generation of such transients are normally associated with the control of pulse transitions. The shortcomings of the prior art RF PIN diode attenuator pulse generators are principally caused by the inability to control the PIN diode to attenuate the RF signals accurately and reliably because of the sharp knee on the PIN diode characteristic curve. A small change in bias current results in a large change in attenuation.
In order to evaluate the design of radio frequency receivers, a means to control the pulse shape of the modulated test signal is required. The required control should independently modify the transition times of the rising and falling edges of the envelope of the modulated RF pulse while minimizing the delay to the signal. In a specific application, the rise and fall transition times should be independently adjustable between 50 and 600 nanoseconds while the total propagation delay is held to less than 25 nanoseconds. Specifically, an RF source in the range of 1 GHz is utilized.
The non-variable pulse modulation in the prior art does not permit a controlled evaluation of the characterisics of RF receivers. Additionally, the transients induced into the modulated signal by the prior art techniques further complicate such evaluation.